The invention relates to carpet seaming irons for applying carpet seaming tape to join sections of carpet together at the backing. More specifically the invention relates to such a carpet seaming iron with temperature control that achieving minimal temperature oscillation during use of the iron.
Carpet seaming tape for attaching sections of carpet together has been well known for several decades. The tape bears a hot melt adhesive which is laid face up beneath the desired joint of the two carpet backings. When a carpet seaming iron at prescribed temperature is pushed over the adhesive and under the carpet edges, melting the adhesive, the carpet sections are seamed together behind the iron by pushing the backings down into the melted adhesive.
The following U.S. patents are directed to features of carpet seaming tape irons: U.S. Pat. Nos. 5,944,943 and 6,172,335.
Carpet seaming tape irons have electric resistance heating elements, under thermostatic or electronic control. When a mechanical thermostat is used temperature oscillation is large. A typical three inch wide iron will oscillate peak to valley about 40° F. for a good quality iron, up to 70° F. for a poorly constructed iron. A typical six inch iron will oscillate 30° to 40° F.
A part of this oscillation is due to the nature of the bimetal thermostat. A bimetal thermostat of the creeper configuration has an on/off differential, or dead zone, of 11° to 25° F., this type being used on most irons. A bimetal thermostat of the snap action configuration has an on/off differential, or dead zone, of 20° to 35° F.
The remainder of the iron is temperature oscillation is caused by overshoot and undershoot. This is dependent on thermal mass of the sole plate, the heater power, and thermal load (hot melt volume).
Temperature oscillation can cause problems in use, for the iron may sometimes be too cool or too hot for effective or efficient use in seaming carpet. A typical optimum temperature is about 390° F., and a high-powered heating element is used to achieve this level of heat. Higher-powered heating elements, and the thermostats used with them, tend toward higher oscillation.
The above referenced U.S. Pat. No. 6,172,335 is directed at the same problem described above, but presents a different solution.